The present invention relates to naphthylisoquinoline alkaloids and derivatives thereof which exhibit in vitro and in vivo antimalarial activity, methods of obtaining useful antimalarial naphthylisoquinoline derivatives, pharmaceutical compositions containing such antimalarial compounds, and methods for using the compounds for the treatment or prevention of malaria. The compounds of the present invention exhibit advantageous pharmacological, toxicological, or antimalarial properties, such as for example, inhibiting in vitro and in vivo the viability, growth, reproduction, and pathological effects of Plasmodia parasites, including drug-resistant strains thereof, which are known to cause malaria.
It is estimated that more than 2-3 million people die of malaria each year, and many more suffer from debilitating infection. Approximately a third of the world""s population lives in malaria-endemic areas, including Central and South America, Asia, and Africa. Transient visitors or workers in these areas also are at ever-increasing risk of contracting malaria. Mosquitoes that carry malaria parasites have become resistant to insecticides, and the deadliest parasites have become resistant to previously effective antimalarial drugs such as chloroquine and other clinically used agents. New effective antimalarial chemotherapy agents are urgently needed. The present invention provides useful new antimalarial compounds and pharmaceutical compositions, as well as methods of using such antimalarial compounds and pharmaceutical compositions to prevent or treat malaria. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The present invention is directed to useful antimalarial pharmaceutical compositions comprised of a suitable, pharmaceutically acceptable carrier and an antimalarial effective amount of at least one naphthylisoquinoline alkaloid selected from the group consisting of dioncophylline B, dioncopeltine A, dioncophylline A, dioncophylline C, dioncolactone A, N-methyl-dioncophylline A, ancistrobrevine D, ancistrocladine, michellamine A, michellamine B, N-methyl-dioncophylline A and atropisomer thereof, 5xe2x80x2-O-demethyl-8-O-methyl-7-epi-dioncophylline A, 4xe2x80x2-O-demethyl-dioncophylline A, dioncophylleine A, (xc2x1)-dioncophyllacine A, hamatine, ancistrobrevine B, ancistrobrevine A, 6-O-demethyl-ancistrobrevine A, ancistrobarterine A, 7-epi-dioncophylline A, N-formyl-ancistrocladine, N-methyl-ancistrocladine, 6-deoxy-N-methyl-ancistrocladine, N-formyl-O,O-dimethyl-dioncophylline C, N-formyl-dioncophylline C, N-formyl-8-O-benzyl-dioncophylline C, N-formyl-8-O-methyl-dioncophylline C, N-formyl-8-O-pivaloyl-dioncophylline C, N-formyl-8-O-acetyl-dioncophylline C, N-formyl-8-O-benzoyl-dioncophylline C, and 8-O-methyl-dioncophylline C, and derivatives thereof wherein one or more phenolic hydroxyl group(s) may instead be an ester, sulfonate ester, or ether group; one or more methyl ether group(s) may instead be a phenolic hydroxyl group; one or more phenolic hydroxyl group(s) may instead be an aromatic hydrogen substituent; one or more secondary amine site(s) may instead be an amide, sulfonamide, tertiary amine, or alkyl quaternary ammonium salt; one or more tertiary amine site(s) may instead be a secondary amine; and one or more aromatic hydrogen substituent(s) may instead be a halogen, nitro, amino, hydroxyl, thiol, or cyano substituent, or a pharmacologically acceptable salt thereof.
The present invention additionally includes a method of obtaining useful antimalarial compounds by applying one or more well-known chemical reactions to a naphthylisoquinoline alkaloid selected from the group consisting of dioncophylline B, dioncopeltine A, dioncophylline A, dioncophylline C, dioncolactone A, N-methyl-dioncophylline A, ancistrobrevine D, ancistrocladine, michellamine A, michellamine B, N-methyl-dioncophylline A and atropisomer thereof, 5xe2x80x2-O-demethyl-8-O-methyl-7-epi-dioncophylline A, 4xe2x80x2-O-demethyl-dioncophylline A, dioncophylleine A, (xc2x1)-dioncophyllacine A, hamatine, ancistrobrevine B, ancistrobrevine A, 6-O-demethyl-ancistrobrevine A, ancistrobarterine A, 7-epi-dioncophylline A, N-formyl-ancistrocladine, N-methyl-ancistrocladine, 6-deoxy-N-methyl-ancistrocladine, N-formyl-O,O-dimethyl-dioncophylline C, N-formyl-dioncophylline C, N-formyl-8-O-benzyl-dioncophylline C, N-formyl-8-O-methyl-dioncophylline C, N-formyl-8-O-pivaloyl-dioncophylline C, N-formyl-8-O-acetyl-dioncophylline C, N-formyl-8-O-benzoyl-dioncophylline C, and 8-O-methyl-dioncophylline C, to provide a naphthylisoquinoline derivative wherein one or more phenolic hydroxyl group(s) may instead be replaced by an ester, sulfonate ester, or ether group; one or more methyl ether group(s) may instead be replaced by a phenolic hydroxyl group; one or more phenolic hydroxyl group(s) may instead be replaced by an aromatic hydrogen substituent; one or more secondary amine site(s) may instead be replaced by an amide, sulfonamide, tertiary amine, or alkyl quaternary ammonium salt; one or more tertiary amine site(s) may instead be replaced by a secondary amine; and one or more aromatic hydrogen substituent(s) may instead be replaced by a halogen, nitro, amino, hydroxyl, thiol, or cyano substituent.
The present invention also encompasses a method of treating or preventing a malaria infection which comprises administering to a mammal in need thereof an antimalarial effective amount of at least one compound selected from the group, consisting of dioncophylline B, dioncopeltine A, dioncophylline A, dioncophylline C, dioncolactone A, N-methyl-dioncophylline A, ancistrobrevine D, ancistrocladine, michellamine A, michellamine B, N-methyl-dioncophylline A and atropisomer thereof, 5xe2x80x2-O-demethyl-8-O-methyl-7-epi-dioncophylline A, 4xe2x80x2-O-demethyl-dioncophylline A, dioncophylleine A, (xc2x1)-dioncophyllacine A, hamatine, ancistrobrevine B, ancistrobrevine A, 6-O-demethyl-ancistrobrevine A, ancistrobarterine A, 7-epi-dioncophylline A, N-formyl-ancistrocladine, N-methyl-ancistrocladine, 6-deoxy-N-methyl-ancistrocladine, N-formyl-O,O-dimethyl-dioncophylline C, N-formyl-dioncophylline C, N-formyl-8-O-benzyl-dioncophylline C, N-formyl-8-O-methyl-dioncophylline C, N-formyl-8-O-pivaloyl-dioncophylline C, N-formyl-8-O-acetyl-dioncophylline C, N-formyl-8-O-benzoyl-dioncophylline C, and 8-O-methyl-dioncophylline C, and derivatives thereof wherein one or more phenolic hydroxyl group(s) may instead be an ester, sulfonate ester, or ether group; one or more methyl ether group(s) may instead be a phenolic hydroxyl group; one or more phenolic hydroxyl group(s) may instead be an aromatic hydrogen substituent; one or more secondary amine site(s) may instead be an amide, sulfonamide, tertiary amine, or alkyl quaternary ammonium salt; one or more tertiary amine site(s) may instead be a secondary amine; and one or more aromatic hydrogen substituent(s) may instead be a halogen, nitro, amino, hydroxyl, thiol, or cyano substituent, or a pharmacologically acceptable salt thereof.
The treatment method of the present invention may also involve co-administering an antimalarial effective amount of chloroquine or other antimalarial agent(s), such as mefloquine, halofantrine, artemisinin, artemether, or quinine, with at least one compound, or pharmacologically acceptable salt thereof, selected from the aforementioned antimalarial naphthylisoquinoline alkaloids or derivatives.
The present invention is predicated on the discovery that certain naphthylisoquinoline alkaloids and derivatives thereof, preferably in substantially pure form, have in vitro and in vivo antimalarial activity, and therefore are useful for antimalarial treatments. Many of these naphthylisoquinoline compounds have chemical formulae, or are derivatives thereof, which have been previously reported in the chemical literature (see Table 1); however, prior to the present invention, none of these compounds were previously known to have in vitro and in vivo antimalarial properties.
The general chemical class of compounds known as naphthylisoquinoline alkaloids are known to occur in plant species of the Ancistrocladaceae and Dioncophyllaceae (see, e.g., Bringmann, The Naphthylisoquinoline Alkaloids, in The Alkaloids, Vol. 29, Brossi, ed., Academic Press, New York, 1986, pp. 141-184). These small plant families occur in tropical Africa and southern and southeast Asia. However, prior to the present invention, no known pure compounds of the naphthylisoquinoline alkaloid class have been known specifically to have in vitro and in vivo antimalarial properties or antimalarial uses.
An arguably somewhat related class of naturally occurring compounds, called bisbenzylisoquinoline alkaloids, has been described, and reportedly has in vitro antimalarial activity (Pavanand, et al., Phytother. Res., 3, 215-217, 1989; Ye and VanDyke, Biochem. Biophys Res. Commun., 159, 242-247, 1989; VanDyke, U.S. Pat. No. 5,025,020, 1991; Lin, et al., J. Nat. Prod., 56, 22-29, 1993; Likhitwitayawuid, et al., J. Nat. Prod., 56, 30-38, 1993; Guinaudeau, et al., J. Nat. Prod., 56, 1989-1992, 1993). However, the latter class is distinctly different from the naphthylisoquinoline alkaloid class of the present invention. Moreover, no in vivo antimalarial activity of the bisbenzylalkaloid class is known; in fact it has been concluded by some authors (e.g., Likhitwitayawuid, et al., supra) that xe2x80x9cbisbenzylisoquinoline alkaloids do not appear to be promising candidates as antimalarial agents.xe2x80x9d
The naphthylisoquinoline alkaloids are chemically unique in several respects. Their basic structure comprises a biaryl system consisting of a naphthalene and a isoquinoline or dihydrogenated or tetrahydrogenated isoquinoline moiety with an unprecedented methyl group at C-3. Moreover, many of these alkaloids display atropisomerism due to the bulky ortho-substituents adjacent to the biaryl axis (Bringmann, supra). Such highly unusual structures presumably result from an unprecedented biogenetic origin, for which a polyketide pathway has been implicated (Bringmann, supra; Bringmann, et al., Planta Med., 57, suppl. 2, 98-104, 1991).
Some naphthylisoquinoline alkaloids in their pure forms have been reported to have interesting biological activities: ancistrocladidine (from A. heyneanus) had pronounced spasmolytic activity (Sharma, et al., Phytochemistry, 14, 578-583, 1975), and ancistrotectorine (from A. tectorius) had antitumor activity (Ruangrungsi, et al., supra). Dioncophyllines A and B were active as fungicides (Bringmann, et al., DE 41 17 080), and dioncophylline A had an antifeedant effect against the larvae of Spodoptera littoralis (Grimm, et al., Planta Med., 58, Suppl. 1, 630, 1992; Bringmann, et al., Phytochemistry, 31, 3821-3825, 1992). However, prior to the present invention, no pure naphthylisoquinoline alkaloid, nor specific pharmaceutical composition thereof, had ever been shown to have in vitro and in vivo antimalarial activity nor to be useful for treatment or prevention of malaria.
Several species from the Ancistrocladaceae and Dioncophyllaceae have been known to be used in the form of crude plant or extract preparations in folk medicine for treatments of malaria. For example, the roots of Ancistrocladus tectorius reportedly have been used for the treatment of malaria and dysentery (Bringmann, et al., Tetrahedron Letters, 31, 639-642, 1990), while other plants, such as Triphyophyllum peltatum, reportedly have been used to treat malaria and elephantiasis (see, e.g., Ruangrungsi, et al., J. Nat. Prod., 48, 529-535, 1985). However, pure antimalarial compounds from such crude plant materials have not heretofore been defined, nor provided specifically in pharmaceutical compositions.
The isolation and chemical identification of pure naphthylisoquinoline alkaloids, including ancistrocladine (Foucher, et al., Plantes Med. Phytother., 9, 26-29, 1975), ancistrocladine, hamatine, ancistrocline (Chen, et al., Yaoxue Xuebaq, 16, 519-521, 1981; Bringmann, et al., Planta Med., 58 (Suppl. 1), 703-704, 1992), and ancistrotectorine (Ruangrungsi, et al., supra), have been reported from the stems, twigs, or leaves of Ancistrocladus tectorius. However, none of these compounds were known to have antimalarial activity, nor were they linked specifically to any antimalarial activity that (presumably) resided in these plants, or extracts therefrom.
Accordingly, the present invention provides antimalarial pharmaceutical compositions comprised of a suitable, pharmaceutically acceptable carrier and an antimalarial effective amount of at least one naphthylisoquinoline selected from the group consisting of dioncophylline B, dioncopeltine A, dioncophylline A, dioncophylline C, dioncolactone A, N-methyl-dioncophylline A, ancistrobrevine D, ancistrocladine, michellamine A, michellamine B, N-methyl-dioncophylline A and atropisomer thereof, 5xe2x80x2-O-demethyl-8-O-methyl-7-epi-dioncophylline A, 4xe2x80x2-O-demethyl-dioncophylline A, dioncophylleine A, (xc2x1)-dioncophyllacine A, hamatine, ancistrobrevine B, ancistrobrevine A, 6-O-demethyl-ancistrobrevine A, ancistrobarterine A, 7-epi-dioncophylline A, N-formyl-ancistrocladine, N-methyl-ancistrocladine, 6-deoxy-N-methyl-ancistrocladine, N-formyl-O,O-dimethyl-dioncophylline C, N-formyl-dioncophylline C, N-formyl-8-O-benzyl-dioncophylline C, N-formyl-8-O-methyl-dioncophylline C, N-formyl-8-O-pivaloyl-dioncophylline C, N-formyl-8-O-acetyl-dioncophylline C, N-formyl-8-O-benzoyl-dioncophylline C, and 8-O-methyl-dioncophylline C, and derivatives thereof wherein one or more phenolic hydroxyl group(s) may instead be an ester, sulfonate ester, or ether group; one or more methyl ether group(s) may instead be a phenolic hydroxyl group; one or more phenolic hydroxyl group(s) may instead be an aromatic hydrogen substituent; one or more secondary amine site(s) may instead be an amide, sulfonamide, tertiary amine, or alkyl quaternary salt; one or more tertiary amine site(s) may instead be a secondary amine; and one or more aromatic hydrogen substituent(s) may instead be a halogen, nitro, amino, hydrokyl, thiol, or cyano substituent, or a pharmacologically acceptable salt thereof (i.e., of the naphthylisoquinoline alkoloids or derivatives thereof).
The present inventive compositions may include other active or inactive components. In particular, they may include other antimalarial agents such as an antimalarial effective amount of chloroquine, mefloquine, halofantrine, artemisinin, artemether, pyrimethamine, quinine, or other antimalarial agent.
Certain chemical modification(s) can be introduced as desired into a given naphthylisoquinoline compound to obtain a new derivative with modified biological properties such as: greater antimalarial potency against a particular Plasmodium sp., a broader spectrum of antimalarial activity against diverse Plasmodia sp., enhanced oral bioavailability, less toxicity in a particular host mammal, more advantageous pharmacokinetics and/or tissue distribution in a given host mammal, and the like. Therefore, the present invention additionally provides methods for obtaining such derivatives by applying one or more well-known chemical reactions to a given naphthylisoquinoline alkaloid selected from the group consisting of dioncophylline B, dioncopeltine A, dioncophylline A, dioncophylline C, dioncolactone A, N-methyl-dioncophylline -A, ancistrobrevine D, ancistrocladine, michellamine A, michellamine B, N-methyl-dioncophylline A and atropisomer thereof, 5xe2x80x2-O-demethyl-8-O-methyl-7-epi-dioncophylline A, 4xe2x80x2-O-demethyl-dioncophylline A, dioncophylleine A, (xc2x1)-dioncophyllacine A, hamatine, ancistrobrevine B, ancistrobrevine A, 6-O-demethyl-ancistrobrevine A, ancistrobarterine A, 7-epi-dioncophylline A, N-formyl-ancistrocladine, N-methyl-ancistrocladine, 6-deoxy-N-methyl-ancistrocladine, N-formyl-O,O-dimethyl-dioncophylline C, N-formyl-dioncophylline C, N-formyl-8-O-benzyl-dioncophylline C, N-formyl-8-O-methyl-dioncophylline C, N-formyl-8-O-pivaloyl-dioncophylline C, N-formyl-8-O-acetyl-dioncophylline C, N-formyl-8-O-benzoyl-dioncophylline C, and 8-O-methyl-dioncophylline C, to provide a derivative wherein one or more phenolic hydroxyl group(s) may instead be replaced by an ester, sulfonate ester, or ether group; one or more methyl ether group(s) may instead be replaced by a phenolic hydroxyl group; one or more phenolic hydroxyl group(s) may instead be replaced be an aromatic hydrogen substituent; one or more secondary amine site(s) may instead be replaced by an amide, sulfonamide, tertiary amine, or alkyl quaternary ammonium salt; one or more tertiary amine site(s) may instead by replaced by a secondary amine; and one or more aromatic hydrogen substituent(s) may instead be replaced by a halogen, nitro, amino, hydroxyl, thiol, or cyano substituent.
The naphthylisoquinoline alkaloids and derivatives, as well as the salts thereof, of the present invention can be used for a variety of in vitro purposes, particularly in assays and the like. These compounds can also be used for in vivo purposes, particularly to prevent and/or treat malarial infections.
The present inventive method of treating or preventing a malarial infection comprises administering to a mammal in need thereof an antimalarial effective amount of at least one of the aforementioned naphthylisoquinoline alkaloids or derivatives thereof, or a pharmacologically acceptable salt thereof (i.e., of the naphthylisoquinoline alkaloids or derivatives thereof). The treatment method may involve the use of the aforementioned antimalarial compositions, and, thus, the treatment method may involve the use of pharmaceutically acceptable carriers and the coadministration of other active or inactive components, in particular, other antimalarial agents such as an antimalarial effective amount of chloroquine, mefloquine, halofantrine, artemisinin, artemether, pyrimethamine, quinine, or other antimalarial agent. The particular infecting malaria-causing organism may be any responsible pathogenic parasite, particularly such as a Plasmodium sp., more :particularly such as P. falciparum, P. vivax, P. malariae, P. ovale, or P. berghei. 
The pharmacologically acceptable salt may be any such suitable salt. Examples of pharmacologically acceptable salts include HBr, HCl, oxalate, citrate, acetate, tartrate, and the like.
By C1-C6 alkyl is meant straight or branched-chain C1-C6 alkyl groups. Examples include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tertiary-butyl, n-pentyl, iso-pentyl, and n-hexyl.
By aryl is meant an organic radical derived from an aromatic hydrocarbon. Examples of an aryl group include phenyl, and o-, m-, and p-hydroxyphenyl.
By aliphatic is meant an organic radical derived from an open hydrocarbon chain. Examples of aliphatic radicals include alkanes, alkenes, and alkynes. Specific examples of aliphatic radicals which can be used in the present invention include, but are not limited to, C1-C6 alkyl radicals, straight or branched.
The aforementioned naphthylisoquinoline alkaloids which may be employed in the present invention have the following structures: 